Switching circuits can fail, including those that use SSRs. When faced with solid state relay problems, you want to quickly find the root cause and get your equipment back up and running. This article aims to explain common SSR problems, how to identify them, and what you can do to solve them.
First, let’s take a quick look at how SSRs work. Then we’ll go over some of the most common issues that plague these devices.
What is a Solid State Relays and How it Works?
A solid state relay, SSR is an electronic switching device that uses semiconductors to switch a circuit on/off in response to an external control signal. A majority of them use photo isolation to provide electrical separation between the input and output.
A photo isolator SS relay uses an LED (light emitting diode) on the input side that turns on when voltage is applied. The light activates a photocoupler on the output side, which then activates the circuit.
SSRs offer reliable switching and can be used in a variety of applications where mechanical relays would typically be employed. This includes household appliances, office equipment, factory assembly lines, in automotive electrical systems and so on.
Common Solid State Relay Problems
As with many other electronic devices, there are a few issues that can crop up during the regular use of solid state relay switching systems. These can range from burnt out relay parts to improper electrical connections. Here are some of the most common solid state relay problems, their causes, and how to solve them.
Solid State Relay Not Working
The relay does not work, even when the control signal is applied. Possible causes for this problem include an open fault at the output element due to the following reasons:
Overcurrent and overvoltage can result from external surges, such as those caused by lightning strikes on power lines. These surges can also come from within the electrical system itself, such as from motor starters or welding equipment causing inrush currents.
With the solid state relay not working, you cannot properly protect your equipment or system. Replace it and make sure to use the correct relay for your application. Also, check and replace any damaged protection devices such as fuses. Make sure all the wires are secure and there are no loose connections.
Solid State Relay Stays On
The solid state relay stays on, even after the input power is removed. In this case, the problem is most likely a short circuit in the load circuit or reset failure: it’s one of the most common issues that electricians encounter when diagnosing the device. Possible reasons may include the following:
- Residual voltage in the load circuit
- Leakage current in input or output
- Inductive noise on input line
- Overvoltage or overcurrent damage
Test the relay for proper operation and if faulty, consider replacing it. You may also want to prevent the problem from happening again by using a better quality relay, installing protection devices such as varistors or snubbers, and by providing a clean power source to the load.
To solve this problem, you need to find and fix the short circuit. This can be done by disconnecting the SSR and testing it. More about how to do that later when looking at how to test SSR relays.
Solid State Relay Overheating
This is one of the most common solid state relay problems and that can have many different causes. So it’s crucial that you understand them and the steps to take. When it comes to the solid state relay, overheating can result from:
- Too much current flowing through the relay
- A bad connection that is causing resistance
- Improper relay installation
- Improper heat dissipation
- Increased ambient temperatures
To fix the problem, you need to find and remove the cause of the overheating. This can be done by using a relay with higher current and voltage rating, improving the connections, or including a varistor in the output circuit. To protect the relay, a fuse is used at the load side.
Ensure, also the correct installation of the relay and that there’s proper air circulation or heat dissipation system. In some cases, it’s necessary to use a heat sink.
How to Test a Solid State Relay
“How do I know if my solid state relay is bad?” Many SSR users have this same question. The answer is “when it stops switching properly”. However, the most accurate solid-state relay troubleshooting method is by testing it.
Testing a solid state relay is a good way to find out if the SSR itself is the problem, plus you can use that to help isolate other issues in your system.
Testing a Solid State Relay (DC-AC)
To test solid state relay devices that use the DC-AC configuration, you will need a DC source of power for the input side and a specified AC load for the output side of the SSR.
Solid state relay input circuits mostly only need to draw a few milliamps, so a 9V battery should work just fine. If you have a DC power supply that’s between 3V and 32V, you may also use that instead.
On the output side of the SSR, connect an AC load that is within the specified range for that relay. A light bulb is a good test load but make sure it is not too much or too little for the SSR you are testing. A bulb rated at least 100W will do.
- Connect the DC power supply (or battery) to the terminals of the SSR, ensuring the correct polarity.
- Connect the load (light bulb) to the AC load terminals of the SSR.
- Apply power to the input of the SSR.
- The light bulb should come on, indicating that the SSR is working properly.
- If the light bulb does not come on, check your connections. If everything is connected properly, the SSR may be defective.
Testing a Solid State Relay (AC-AC)
To test an AC-AC solid state relay, you will need an AC source of power for the input side and an AC load for the output side of the SSR. You may use a mains outlet for the input power. For the SSR output side, an AC motor is usually a preferred load.
- Connect the input power source and load, just as you would when testing a solid state relay with DC inputs.
- Upon switching on the input control current, you should see the motor start running, indicating that the SSR is working properly.
- If the motor does not run, the relay may be bad.
Solid State Relay Replacement
When a solid state relay fails, it needs to be replaced. This can be done by matching the replacement SSR to the specifications of the original. To do this, you need to know the following:
- The type of output required (AC or DC)
- The voltage and current ratings of the SSR
- The input/output connection type
- The mounting method (surface, DIN rail etc.)
Solid state relay replacement should be done by a qualified person. That’s because proper wiring and handling of the SSR is essential to its proper function and long life.
Also, make sure that the surrounding area is clean and free of dust, as this can contribute to problems with the solid state relay. Check out this solid state relay wiring video for more information on its proper installation.
SSR relays are simple devices that can be used to control a variety of loads. However, like all electronic devices, they can sometimes fail. To fix solid state relay problems, you need to find their cause. This can be done by testing the relay and making sure the connections are good. If you have a solid state relay that is not working properly, the steps in this guide will help you to troubleshoot the problem.